A device such as a vehicle driven upon receiving liquid fuel such as a gasoline engine or a diesel engine has a fuel tank storing fuel, a fuel pump module is installed in the fuel tank and connected to an engine through a fuel supply line to supply the fuel stored in the fuel tank to the engine. A fuel pump is provided in the fuel pump module in order to press-feed the fuel filling the interior of the fuel tank toward the engine.
Here, a general fuel pump has a single impeller configured to be rotated, and a fuel pump used in a fuel supply device for liquefied petroleum gas (LPG) such as a liquid phase LPG injection (LPLI) fuel system needs to press-feed fuel at high pressure of 5 bar or higher, and thus, to this end, the fuel supply device for LPG uses two fuel pumps or uses two stages (two impellers are provided in multiple stages) in a single fuel pump.
However, the use of two fuel pumps together causes a side effect such as beating noise due to the combination of the same two fuel pumps, and in the case of the two-stage fuel pump in which impellers are provided in multiple stages, as impellers having the same specification are applied to first and second stages, noise is amplified to be doubled at the same frequency. That is, in a related art multi-stage fuel pump in which a plurality of impellers are provided in multiple stages as illustrated in FIG. 1, two impellers having the same diameter and the same number of blades (having same shape) are applied, increasing BPF noise to fail to satisfy required noise standard.